The present invention relates to a control system for a transmission.
U.S. Pat. No. 4,735,113 discloses a V-belt type continuously variable transmission including a driver pulley, a folower pulley, and a V-belt drivingly interconnecting these pulleys. Laid-open Japanese Patent Application 63-176862 and U.S. patent application Ser. No. 07/278,887 disclose a transmission in which the above-mentioned continuously variable transmission mechanism is combined with a gearing mechanism such that the gearing mechanism plays a role in providing a reduction ratio larger than the largest reduction provided by the continuously variable transmission. In the continuously variable transmission of the type using a V-belt, the V-belt slips upon acceleration after rapid deceleration, causing a damage on the V-belt. The V-belt is disposed in pulley grooves of the driver and follower pulleys. The width of each of the pulley grooves is variable by varying hydraulic fluid pressure supplied to the pulley. At rapid deceleration, hydraulic fluid pressure supplied to the driver pulley is decreased to allow an increase in the width of the pulley groove thereof, causing a shift toward the largest reduction ratio. Upon acceleration immediately after this rapid deceleration, hydraulic fluid pressure supplied to the driver pulley is not high enough to generate a gripping force with which the driver pulley grips the V-belt. However, the driver pulley is subject to a large torque before there occurs a sufficient friction between the V-belt and the driver pulley. Thus, a slip occurs between the V-belt and the driver pulley. This problem is encountered in the latter mentioned hybrid transmission including the continuously variable transmission mechanism combined with the gearing mechanism.
The present invention aims at improving a control system for a transmission including a gearing mechanism combined with a continuously variable transmission such that the above-mentioned problem is not encountered.